Oak Ridge Experiment on CO2 Enrichment of Sweetgum



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Site Description

The research site is a planted sweetgum (Liquidambar styraciflua) monoculture located on the Oak Ridge National Environmental Research Park (35o 54' N; 84o 20' W) in southeastern United States. Oak Ridge is in eastern Tennessee in the Ridge and Valley province between the Cumberland and Blue Ridge Mountains. 

Plantation Establishment
The plantation was established in spring, 1988, on an old terrace of the Clinch River (elevation 230 m). One-year-old, bare-rooted sweetgum seedlings were planted at a spacing of 2.3 m × 1.2 m.  There is a total of 1.7 ha planted with sweetgum in two areas � a 185 × 70 m area and a smaller 85 × 50 area, separated by a stand of sycamore (Platanus occidentalis) that was used in a N nutrition experiment  (van Miegroet et al. 1994). No fertilizer has been added to the sweetgum; herbicide was used in 1989 and 1990 to control competition from weeds.

Stand Characteristcs
When the experiment was initiated in 1997, stand basal area was 29 m2/ha with an average tree height of 12.4 m and stem diameter of 11.3 cm.  The height and basal area are very uniform across both areas planted in sweetgum. The sweetgum stand has a closed canopy with a leaf area index of 5; lower branches are self-pruning and there is some mortality of suppressed trees.

The understory was very sparse when the experiment was started in 1997 but has become more aggressive since then. Important species include an invasive C4 annual grass (Microstegium vimineum), non-native, invasive woody plants (Lonicera japonica, Ligustrum sinense), and other taxa. Tree seedlings, including Acer negundo, Acer rubra, Liriodendron tulipifera, Quercus alba, are sparse.

The soil at the site, which is classified as Wolftever, an Aquic Hapludult, developed in alluvium washed from upland soils derived from a variety of rocks including dolomite, sandstone, and shale.  It has a silty clay loam texture and is moderately well drained (SCS 1967, van Miegroet et al. 1994).  The soil is slightly acid (water pH approximately 5.5-6.0) with high base saturation largely dominated by exchangeable Ca.

bulk density           1.5 g/cm3
C content               74 Mg/ha
N content               11 Mg/ha
extractable P          82 kg/ha
exchangable K      663 kg/ha
exchangable Ca   7670 kg/ha
exchangable Mg   1040 kg/ha

The climate is typical of the humid southern Appalachian region. Mean annual temperature is 14.2°C and mean annual precipitation is 1390 mm. Precipitation is generally evenly distributed throughout the year.

More Oak Ridge climate data are available from the Atmospheric Turbulence and Diffusion Division

Soil Conservation Service. 1967. Soil survey and laboratory data and descriptions for some soils of Tennessee.  Soil Survey Investigations Report No. 15, U.S. Dept. Agric., Soil Conservation Service and Tennessee Agricultural Experiment Station.

van Miegroet, H., R. J. Norby, and T. J. Tschaplinski. 1994. Optimum nitrogen fertilization in a short-rotation sycamore plantation.  Forest Ecology and Management 64:25-40.

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Last revised: June 27, 2009